The present invention relates to an oil supply device of an engine equipped with a variable valve-drive mechanism which selects valve characteristics by using operational oil supplied through one of lash adjustors respectively provided at valve drive portions located on an intake side and an exhaust side.
Conventionally, a valve drive mechanism of an engine, in which lash adjustors are provided at valve drive portions of the engine and oil is supplied to the lash adjustors from an oil-pressure supply system including an oil pump as operational oil to automatically adjust valve clearances, is known as shown in Japanese Patent Laid-Open Publication No. 5-306603.
The oil pressure supplied to the lash adjustors is required to be maintained at an appropriate value so that the performance of the valve drive portions can be proper. Then, according to the device disclosed in Japanese Patent Laid-Open Publication No. 2008-106701, for example, a properly-high oil pressure supplied to the lash adjustors can be ensured by stopping or restricting some oil supplying to the other parts than the lash adjustors when the oil pressure of the oil-pressure supply system decreases.
Further, some engines equipped with a variable valve-drive mechanism which selects valve characteristics, such as valve lift or valve timing, in accordance with an engine running condition are known as well. In some type of engines among these, the valve characteristics are selectable by supplying the operational oil through the lash adjustors at the valve drive portions (see US Patent Application Publication No. 2008/230023, for example).
In the case of supplying the operational oil to the variable vale drive mechanism through the lash adjustors at the valve drive portions as shown in the above-described US patent document, there is a problem in that when the valve characteristics are selected by the variable vale drive mechanism (to decrease the oil pressure), the pressure of the oil supplied to the lash adjustors decreases accordingly, so that the valve clearances may not be kept at an appropriate value. Herein, since it is required to decrease the oil pressure quickly for a prompt selection of the valve characteristics, it may be considered that the oil passage to supply the oil pressure to the lash adjustors is made open so as to connect to a drain oil passage by a valve, for example. In this case, however, the oil pressure supplied to the lash adjustors may decrease extremely. Thus, the requirement of the oil pressure for the selection of the valve characteristics is substantially different from the requirement of the oil pressure for the lash adjustors, so there was still some room for improvement in order to meet the both requirements.